The present invention is directed to the electrical charging art and in particular, to a battery charging system which includes control circuitry for maintaining a full charge on, but not over charging, a battery.
There are numerous applications in which the battery powered or battery dependent system is left unattended for extensive periods. Examples are infrequently used vehicles such as automobiles, motorcycles or boats. A battery left in an unattended state will gradually lose its charge and suffer cell to cell variations arising from temperature differences between cells or impurities and minute differences in the cells themselves. A prolonged battery undercharged state causes the plates to sulfate and results in a permanent loss of battery capacity. This degradation mode can only be avoided by periodic recharging of all cells. Further, periodic recharging assures that the battery is charged to a state such that its suitable for its intended purpose, such as providing sufficient current to start and run an associated engine.
While charging systems known to the prior art are capable of charging a battery, they suffer from numerous disadvantages.
Charging beyond the batteries maximum capacity can significantly degrade battery life. Over charging can lead to corrosion of the plate grids and result in excessive gassing, which shortens cell life. Thus, once the battery becomes charged to its full capacity, the charging current should cease. Not even a trickle or "topping" charge is permissible.
Even though a battery is not charged beyond it maximum charge capacity, it may be charged at a rate that is excessive and leads to shortened battery life. A high charge rate can increase electrolyte temperatures to above 125.degree. Fahrenheit and result in gassing and corresponding cell degradation. Charging systems, however, charge at high rates as an apparent convenience to the user, thereby shortening battery life.
As a battery approaches its full charge state, the charge rate should be tapered to prevent gassing. While this feature is often provided in prior charging systems, as described above it is imperative for long battery life that the charge rate completely cease when the battery becomes fully charged.
Batteries have been known to short, and installers have been known to short the output from battery chargers or, worse yet, reverse the charger connections to the battery. Probably the single largest cause for the failure of chargers is transformer overheating due to a short or near-short at the charger output.
In charger applications involving high ambient temperatures, the problem of transformer heating is further exacerbated also leading to improper operation, or failure of prior art chargers. The charging indicating systems typically provided with prior art chargers are inadequate at best and often misleading. The common indicator is an ammeter which indicates current flow to the battery. Such flow does not necessarily reflect the state-of-charge of the battery, which is the crucial measure of whether the battery requires further charging.
A further problem with prior-art chargers is that they require manual supervision. A typical charger requires an operator to hook up the system, remembering to remove the connection to other associated circuits to eliminate the possibility of spikes from the charger damaging electronic equipment. The charger is then left on for a period of time and must be manually disconnected. The potential for the charger to drain the battery during periods when the charger is turned off, coupled with the above related problem of an operating charger damaging electrical equipment which is normally coupled to the battery, has required that prior-art chargers be manually disconnected from the battery when not in use.
Further, prior art chargers are large, bulky and heavy items such that even if they were electrically suited to be permanently connected to a battery, such connection would not be practical.